Total property

How can I sum and save the property Total into database?

public partial class CartItem : Entity<Int64>
  {
    private Int64 _orderId;

    private Int64 _productId;

    private decimal _quantity;

    private decimal _price;

    private decimal _total;

    public Int64 OrderId
    {
      get { return Get(ref _orderId, "OrderId"); }
      set { Set(ref _orderId, value, "OrderId"); }
    }

    public Int64 ProductId
    {
      get { return Get(ref _productId, "ProductId"); }
      set { Set(ref _productId, value, "ProductId"); }
    }

    public decimal Quantity
    {
      get { return Get(ref _quantity, "Quantity"); }
      set { Set(ref _quantity, value, "Quantity"); }
    }

    public decimal Price
    {
      get { return Get(ref _price, "Price"); }
      set { Set(ref _price, value, "Price"); }
    }    

    public decimal Total
    {
      get { return Get(ref _total, "Total"); }
      set { _total = Quantity * Price; Set(ref _total, value, "Total"); }
    }
}

tks.

Update Total as part of updating either the Quantity or Price, e.g.

public decimal Quantity
{
  get { return Get(ref _quantity, "Quantity"); }
  set 
  { 
    Set(ref _quantity, value, "Quantity"); 
    Total = Quantity * Price;
  }
}

public decimal Price
{
  get { return Get(ref _price, "Price"); }
  set 
  { 
    Set(ref _price, value, "Price"); 
    Total = Quantity * Price;
  }
}  

public decimal Total
{
  get { return Get(ref _total, "Total"); }
  set { Set(ref _total, value, "Total"); }
}

Jeremy